Method of finshing aromatic concentrates



METHOD OF FINISHING AROMATIC CONCENTRATES Filed April 10, 1947 FreshSulfuric Acid |8 Aromatic Extract cuusi'c Fresh Guus1ic lnhibiior v s NI i I 42 my 07 as v mm? a" 5| l 4- e 52 4 5 l 39 Fresh/ v CuusficFinished Aromatic Concentrate 43 49 4 47 37 38' L 8 40 Hclner SpentCushc M d 1/ INVENTORJ:

BY I

Qfl/W AT OR/NEY- Patented Sept. 13, 1949 UNITED STATES PATENT OFFICEMETHOD OF FINISHING AROMATIC CONCENTRATES tion'of Delaware ApplicationApril 10, 1947., Serial No. 740,564

2 Claims.

This invention relates to a method of finishing aromaticconcentratescontai'ning appreciable quantities (1.0% or over) ofolefinic compounds.

This invention is particularly adaptable to the finishing of syntheticaromatics produced by the catalytic dehydrogenation of cyclonaphthenesin which process undesirable by-products such as .olefinic compounds areformed which. render the concentration and finishing of the aromaticconcentrate a difficult operation.

synthetically produced aromatics resulting from a catalyticdehydrogenation process may be concentrated by distillation and thensubjected to. liquid sulfur dioxide extraction wherein an extractisproducedcontaining from 70% to 90% aromatics, from.5% to 29% of highboiling paraflinic compounds and from 1% to 5% olefinic may be treatedto remove harmful olefinic bodies by acid-treating the oil, neutralizingthe acidtreated' oil with a concentrated. aqueous solution of causticalkali, heating the oil to an elevated temperature. and .hydrol'yzing itwith an aqueous Ti;

solution of caustic alkali, and subsequently distilling the treated oilvunder controlled conditions 'to. produce a stable nitration gradetoluene concentrate. This process is disclosed and claimed in U. S.Patent 2,400,373;

Although the above-mentioned process has beenfbund to be particularlysuitable for finishing nitration grade toluene concentrates, it is notapplicable for finishing all types of aromatic concentrates. Forexample, the higher boiling aromatics such as the xylenes may be treated'by the above-mentioned process to produce a concentrate which is notentirely satisfactory ,from thestandpoint of stability. It is alsosometimes desired to produce an even more stable toluene concentratethan is produced by the above-described procedure.

It is the main object of the present invention to provide a method fortreating an aromaticcontaining oil. I

It is a further object of this invention to trea aromatic-containingoils by a'procedure permit- ,tingtheproduction oi. an aromaticconcentrate having improved stability characteristics.

Briefly, our invention comprises acid treating an aromatic-containingfraction under controlled conditions to remove substantial portions ofolefinic compounds, separating acid sludge from. the treatedv material,neutralizing easily neutralized constituents in the acid treatedmaterial in the presence of an alkaline solution, hydrolyzing thealkaline washed material at elevated temperatures and carefullycontrolled contact times with an alkaline solution of carefully adjustedconcentration, separating the hyclrolysed material, adding to it analkaline material and distilling it under carefully controlledconditions such that acidic materials released during the distillationare neutralized and recovering an aromatic concentrate from thedistillation operation which is inhibited with a phenolic material toobtain an aromatic concentrate of improved stability characteristics.

We have found that an aromatic containing fraction of the characterabove-described may be treated to improve its stability to a desireddegree by a process including the following steps. The temperature ofthe extract from the sulfur dioxide extraction process is adjusted toapproximately 80 F. and the extract is then acid treated in a two-stageacid treater, Fresh su'lfuric acid is employed in the second stage andacid sludge withdrawn from the second stage is utilized to pretreat theextract in the first stage. Following the acid treatment, caustic sodasolution of from 18 to 20" B. is employed to neutralize the acid oil.The neutralized acid oil is then hydrolyzed at a temperature in therange of 300 to 325 F. in the presence of18 to 24 B. caustic sodasolution and then separated fromthe caustic soda solution by settling.The hydrocarbon material withdrawn from the settling stage is admixedwith saponified petroleum phenols or sodium naphthenates and distilledto remove an aromatic concentrate as a condensate fraction. Thecondensate fraction is then inhibited by the addition of petroleumphenols or other inhibitor and a finished aromatic concentrate ofimproved stability is thus obtained.

The operation of the hydrolyzing step in the above finishing procedureis of prime importance. Two different types of sulfonated material arecontained in the finished extract charged-to this unitv These are thealkyl sulfates which are easily hydrolyzed in'thepresence of steam orhot caustic and the aromatic sulfonates and chemically neutralsulfonated compounds which are extremely difficult to hydrolyze by steam.or hot caustic. It is necessary to remove both types of sulfonatedcompounds or to neutralize them in pipe 35 to vessel 36.

the distillation step in order to prevent the liberation of free sulfurdioxide in the distillation step which will be contained in the finishedaromatic concentrate and which will render this contaminated concentrateunstable in storage with respect to acid wash color and sometimesoriginal color.

In order to explain the present invention more fully, the preferredtreating procedure will be described in conjunction with the drawing inwhich the single sheet is in the form of a diagrammatic fiow sheet.

Referring now to the drawing, an aromaticcontaining mixture such as isobtained from a sulfur dioxide extraction plant is passed through line II to incorporator I2, acid sludge being introduced into the liquidstream flowing through line II by means of line I3. An admixture of acidsludge and the aromatic-containing stock is withdrawn from incorporatorI2 by line I4 and passed into settling vessel I5. An acid sludge layeris withdrawn from vessel I5 by line I6 and a hydrocarbon fraction iswithdrawn by line H, admixed with fresh acid from line I8 and passedinto incorporator I9. where thorough admixture of the .through line I3containing pump 22 and the hydrocarbon fraction is withdrawn by line 23,has .an alkali metal hydroxide solution such as caustic solution addedthereto by line 24 and passes into incorporator 25. A mixture of causticand hydro carbons is withdrawn from the incorporator 25 by line 26 andpasses into settling vessel 21. Caustic from the lower portion of vessel21 is withdrawn through line 24 and is recycled by means of pump 28. Ifdesired, spent caustic may ;be withdrawn from the recirculating line byoutlet 29 and fresh caustic may be added to the recirculating line byinlet 30.

. The hydrocarbon fraction from vessel 21 may be withdrawn through line3| to intermediate storage vessel 32. Hydrocarbon from vessel 32 iswithdrawn through line 33, sent through preheater 34 where it is heatedto a temperature in the range of 300 to 325 F. and then passed by Vessel36 is arranged to allow intimate contacting .of immiscible fractionstherein and the settling of said fractions and to this end is providedwith recirculating line 31 containing pump 38, and heater 38; line 31discharges into vessel 36 through spray nozzles 39.

Recirculating line 31 is provided with outlet 40 aromatic-containingfraction injected into vessel 36 with 18 to 24 Be. caustic which isdispersed through spray nozzles 39 at a high velocity.

4. Heater 38' may be used to maintain the temperature of the mixture inthe drum at the desired operating temperature of 300 to 325 F. Theretention time of the aromatic-containing fraction in the mixing sectionof the drum must be a minimum of ten minutes. After the mixing periodthe hydrocarbon caustic mixture is conducted to the settling section ofthe drum wherein. the two phases are allowed to separate. Thearomatic-containing fraction is withdrawn from the vessel continuouslyby means of line 42.

To obtain an aromatic fraction of satisfactory stability, the chargewithin vessel must be maintained in intimate admixture with the causticsoda for a minimum period of ten minutes and the total time ofcontacting and settling must not be less than 1 hour at 300 F. orone-half hour at 325 F. It is preferable to renew the caustic sodasolution'in vessel 36 when its total sulfate content has increased to40,000 parts per million although, if desired, the sulfate content maybe allowed to increase to 60,000 parts per million before the renewalstep. In ordinary op-' erations the caustic must be renewed when from300 to 500 barrels of aromatic extract have been treated per barrel ofcaustic. The aromatic containing fraction passing through line 42 hasadded to it a portion of saponified petroleum phenols, sodiumnaphthenates, or other basic material from line 41, pump 48, and line49. The quantity of 'saponified petroleum phenols or other materialadded through line 49 will vary depending on the tendency of thematerial undergoing distillation to release sulfur dioxide. As a rule,it is desired to add from 30 to 50 gallons of such material per 1,000barrels of concentrate. The concentrate containing the saponifiedmaterial then passes into distillation zone 43 where it is separated bydistillation. A light overhead fraction may be removed from the zonethrough line 44,.a side stream consisting of the desired aromaticconcentrate is removed via outlet 45 and a bottoms fraction is removedthrough line 46. To prevent excessive decomposition of sulfonatedcompounds in the distillation column, it is desirable to heat thehydrocarbon fraction no higher than about 525 F. in the distillationzone. This is true even though an alkaline material is present in thehydrocarbons undergoing distillation.

It is to be understood that zone 43 may comprise one or more precisefractionation towers. For example, this zone may comprise two efiiclentdistillation towers with the finished aromatic concentrate beingrecovered as an overhead fraction from the second of the two towers.Inhibitor, such as petroleum phenols, is withdrawn from tank throughvalve 5| and line 52 to combine with the aromatic concentrate passingthrough line 45.

' centrate may be withdrawn through line 53m a suitable storage meansnot shown. Usually approximately two to fifteen pounds of inhibitor per1000 barrels of the finished aromatic concentrate is suflicient toinsure the production of a stable product. 7

The amount of sulfuric acid employed in the acid treating step willdepend on the molecular weight of the aromatics being treated and on theamount of olefinic materials. contained in the The finished stabilizedaromatic conbromine number barrel. In other words. its. stock has a5bromine number and is acid treated with 25 pounds of acid per barrelofstock, the acid treat is 5 pounds of acid per bromine number barrel. Atypical benzene concentrate usually requires as little as one to twopounds of acid per bromine number barrel and a toluene concentrate, from2.5 to 3 pounds of acid per bromine number barrel. Cs and C9 aromaticsusually require approximately 4 to 5 pounds of acid per bromine numberbarrel and the higher boiling aromatics will require more acid perbromine number barrel depending on their molecular weight and the easewith which they sulfonate.

As previously mentioned, the alkaline material added to the concentratein line 42 may suitably be a partially or completely saponifiedpetroleum phenols fraction such as sodium phenolates or may comprisealkali metal salts of naphthenic acids derived from petroleum fractions.The chief function of this material is to neutralize sulfur dioxideformed during the distillation step from acidic materials not removedduring the hydrolysis operation. The inhibitor added to the distilledaromatic concentrate may suitably be petroleum phenols, an amino phenol,such as N- butyl-p-aminophenol, or a phenylenediamine, such asN,N-di-sec-butyl-p-phenylenediamine or their mixtures. V

A typical example of a treatment of an arcmatic-containing fractioncomprising predominately Ca and C9, aromatics resulting from catalyticdehydrogenation will now be given. A fraction having a boiling range of250 to 500 F. and consisting of 75.4% aromatics, 20% parafliniccompounds, and 4.6% olefinic compounds with a bromine number of 5.8 wastreated with 25 pounds per barrel of 96% sulfuric acid. The acid-treatedoil was then contacted with 20 B. caustic soda solution in an amountequivalent to about 4.3 pounds of sodium hydroxide per barrel of oil.The aromatic-containing charge was then heated to a temperature of about315 F., admixed with 1.5 volumes of 20 B. sodium hydroxide solution at atemperature of 325 F. and kept in intimate contact therewith for tenminutes in the mixing zone of the hydrolyzer drum. The caustic wasseparated from the mixture in the settling drum of the hydrolyzer andthe aromatic-containing fraction was withdrawn from the hot causticsolution after a total contact and settling time of about one-half hourat 325 F.

A portion of the aromatic concentrate was then distilled to separate afraction containing 99% aromatics and having a bromine number of 0.1.The distilled aromatic concentrate was then tested for acid wash color.An accelerated oxidation test was then made in which the hydrocarbonswere heated for various periods of time in the presence of anoxygen-containing gas under carefully controlled conditions, and theacid wash color was again tested. The results of these tests are shownas follows:

Acid wash color Original 1-2 Accelerated oxidation test-after- 4 hours6-7 8 hours 8-9 12 hours 9-10 16 hours 9-10 20 hours 12-13 24 hours 14 Asample of the distilled aromatics was also placed in storage for aperiod of 19 days after whichtime' the acid-Wash color-divas found "tohave increased from 1-2 to 11.

The acid wash color of the aromatic concentrate was determined byagitating 21 cc. of the concentrate with 7 cc. of Water white 96%sulfuric acid for 20 seconds in a 30 cc. square bottle. The mixture wasthen settled for 15 minutes and the color of the acid layer comparedwith the color of a series of standard solutions. An acid wash color of6-7 indicates that the color of the acid layer is intermediate the colorof standards 6 and 7. The higher the color, the poorer the stability ofthe oil being treated. l

The accelerated oxidation test-is carried out by placing 500 cc. of oilin a one liter, roundbottom flask and placing the flask in a bathmaintained at a temperature of about 200 F. Air is bubbled through theoil in the flask at a carefully controlled rate for 24 hours. Every 4hours during the oxidation perioda sample of the oil is removed andtested for acid wash color.

It is seen that the aromatic concentrate .-finished by the aboveprocedure was very unstable since the acid wash color should not beabove about 4 after 24 hours accelerated oxidation.

Another portion of the sample of distilled concentrate was inhibitedwith petroleum phenols and the acid wash color of the inhibited productwas tested after being subjected to an accelerated oxidation test forvarious periods of time. The results of these tests are shown asfollows:

Petroleum phenols, lb./1000 bbl. 2 10 a 7 Acid wash color Original .1 21-2 Accelerated oxidation test after- 4 hours 2' V 2 8 hours 3-4 2 12hours 5 2 16 hours 5 2 20 hours 5-6 4 24 hours 6 I 4-5 It is seen thatthe addition of from 2 to 10 pounds of inhibitor per 1000 barrels of thearcmatic concentrate greatly improved the stability of this material.

A portion of the hydrocarbons subjected to the above caustic hydrolysisprocedure was then distilled in the presence of 39 gallons of saponifiedpetroleum phenols per 1,000 barrels of feed and the resulting aromaticconcentrate removed from the distillation tower was inhibited with 10pounds of petroleum phenols per 1000 barrels. The inhibited concentratewas then subjected to an accelerated oxidation test and the acid washcolor of the concentrate was determined after various oxidation times.These tests are shown It is seen that the distillation of theconcentrate in the presence of saponified petroleum phenols combinedwith the inhibiting operation produced a finished concentrate which ismore stable than that produced by distilling without the addition ofpetroleum phenols followed by inhibiting the material.

ates-n t it is; mentioned. that increasing the acid treat. in the aboveexample; 130144} pounds of acid per barrel produced a. concentrate whichafter caustic treating, hydrolysis, and distilling was not improved inacid wash color as compared to that treated with 25- pounds of acid perbarrel. It is indicated, therefore; that the critical phase of thetreating procedure is that of preventing sul fur dioxide from carryingover into the finished aromatic concentrate inappreciable quantities andof inhibiting the finished aromatic concentrate; to prevent any small.quantities of acidic materials therein from deleteriously effecting thestability of the finished product.

Having fully described. the present invention, what we wish to claim is:

1. A. process for the treatment oi a hydrocar bod. oil comprising amajor portion of aromatics and a minor portion of olefins including thesteps of admixing said oil with concentrated. sulfuric acid atapproximatelyatmospheric temperature to form an acid sludge andseparating the acid sludge: therefrom, subsequently admixing said oil.with. caustic soda solutionof 18 to- 200'B.at approximately atmospherictemperature and separating said oil: from said caustic soda solution,heating the oil to a temperature in the range of 300:to: 325 Eh,intimately contacting said oil with caustic soda solution. of 18: to 24B; for less than ten: minutes and. subsequently separating the hotcaustic soda. solution. from the oil. with. a total contacting andseparating time of not less than one hour at 300 F;, adding to saidseparated oil an alkali metal salt of petroleum naphthenic acids,distilling said mixture at a temperature no higher than 525 F;, removingan aromatic concentrate as a side stream from said distillation, andinhibiting said aromatic concentrate.

2. A process for the treatment of a hydrocarbon oil comprising a major'portion Cs and C9 aromatics and a minorportion of olefi'ns inciuding thesteps of admixing said oil with concentrated sulfuric acid atapproximately atmospheric tem- Number 8i 7 perature: to term. an acid;sludge. andseparating the acid sludge therefrom, subsequently admixmg.said oil; with caustic soda solution, of 18 to 2(1 v at approximatelyatmospheric temperature: andseparati-ng said oilfrom said. caustic sodasolution, heating the oilto: a temperaturei-n the range ofp300 to 325?R, intimately contacting said oil with. caustic soda solution of 18 to241 B. for no less than ten minutes and subsequently separating the hotcaustic soda solution. from the oil with a total contacting andseparating. time oi not less than one-half hour at 325 F., admixing saidseparated oil with from 30 to 50 gallons of an alkali metal salt ofpetroleum. naphthenic acids per 1009 barrels of oil, distilling saidoil. at a temperature no higher than 525 removing alow boiling fractionas overhead and a desired aromatic-containing fraction as a side stream,and addingto: said aromatic-containing fraction from 2 to 15- pounds ofa phenolic inhibitor per 1000 barrels of said. fraction.

- 7 JOHN BROWDER...

ROBERT M. LOVE. HENRY G. SCHUTZE. RICHARDiE. TANNICH.

REFERENCES CITED The following references are of record in the file ofthis patent:

sTa'rEs PATENTS Name Date v Chappel'l June-3 i930 Pew July 2, 1 935 PottMar; l0, 1-936 Schutze May 14, 1 946 et Bil V Sept. 24-, 1946 FQREIGN-PATENTS 1 Comtry 7 Date Great Britainv n m. Aug. 7, 1934 Number1,761,328" 2 30063407 2 ,033,297 2,400,373 24U80l3t Certificate ofCorrection Patent No. 2,481,816 September 13, 1949 JOHN G. BROWDER ETAL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: 1 Column7, line 24, for 18 to 200 Be. read 18 to 20 B.;

and that the said Letters Patent should be read with this correctiontherein th.aLthe/ same may conform to the record of the casein thePatent Ofiice. I

Signed and sealed this 31st day of January, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommz'sm'oner of Patents.

